The present invention is an improvement over the envelope and sheet feeding apparatus disclosed in U.S. Pat. No. 3,934,868. As disclosed therein, the feeding apparatus includes three widely spaced suction cups supported on individual arms movable between an initially lowered position and a raised position where the suction planes of the suction cups are parallel to and engage the bottom exposed surface of the bottommost sheet in a stack of the same held in a top loadable stacking frame, so that the operation of the apparatus does not have to be interrupted when the supply of sheets is to be replenished. The stack of sheets preferably rests on a slightly forwardly inclined support tray which terminates short of the lower front end of the stack to leave an opening running the entire width of the stack to expose thereat the bottom sheet in the stack for engagement by one or more of the suction cups. The front end of the stack rests on a rigid support ledge so that when the bottommost sheet is pulled from the stack by the lowering of the suction cups, the weight of the stack above the same will tend to maintain this next sheet within the stacking frame. The suction applied to the suction cups is released in the lowermost position thereof where the sheet is applied to a feed or drive roller which directs the sheet to other sheet feeding apparatus.
One of the features of the present invention is the unique manner in which the suction cups of the sheet feeding apparatus of the invention are positioned with respect to a ledge which, in the most advantageous form of the invention, is flexible, to ensure withdrawal of only one sheet thereby from the bottom of the stack. To best appreciate this feature, it is helpful first to understand the suction cup orientations of the patented apparatus now being described. Thus, each of the suction cups disclosed in this patent is carried upon a lever pivotally mounted upon the end of a pivoted link. Each lever is urged by a coil spring toward a shoulder on the link, so that, unless an external force is applied thereto, the suction cup has a fixed orientation with respect to the lever. As the pivoted lever is rocked in one direction, the suction cup is moved between a lowered position, where the plane of the cup mouth (to be referred to as the suction plane) is tilted downwardly toward the front of the stack at a substantial angle to the plane of the bottommost sheet in the stack, and a raised position where the suction plane is parallel thereto. In this lowered position, the suction cup-carrying lever abuts a shoulder which supplies an external force which tilts the lever on the link and positions the suction plane of the suction cup at a greater angle than it would otherwise have, so that the suction cup can position a sheet withdrawn from the stack thereby against the top of a drive roller, before a pressure roller is brought against the top of the sheet to press the sheet upon the drive roller. As the link carrying the suction cup lever nears a fully raised position, the suction cup lever leaves contact with the abutment shoulder, so that the lever assumes a normal position where it is urged against said shoulder on the link. When the suction cup makes initial contact with the bottommost sheet in the stack, the suction planes of the suction cups are parallel to the sheet. The linkage carrying the suction cup lever then moves in a direction which both tilts the angle of the suction cup mouth away from the support ledge and moves the same in a direction having a substantial horizontal component parallel to the sheet and away from the support ledge. Where a rigid sheet material is involved, this bodily movement parallel to the sheet sometimes causes the suction cup to slip from the sheet. Where suction contact with the sheet is maintained, this tilting and horizontal movement of the suction cup followed by downward movement thereof pulls the front end of the sheet clear of the support ledge. While this equipment works very well with flexible sheet material, there is the problem described where rigid sheets are involved. The further downward movement of the suction cup reestablishes contact of the suction cup lever with said shoulder, which pivots the lever and the suction cup in the opposite direction.
Accordingly, one of the objects of the invention is to provide a unique support structure for varying the angle of tilt of the suction cups in a unique manner which enables them reliably to withdraw only the bottommost sheet from a stack of sheets whether the sheet involved is rigid or flexible.